There is conventionally proposed an on-vehicle speaker device (a speaker system for a mobile object) which is placed in an instrument panel of a vehicle and also utilizes sound emitted from the back side (for example, refer to Patent Literature 1). In a conventional on-vehicle speaker device described in Patent Literature 1, a speaker is installed in an instrument panel with its front side set at an upper surface of the instrument panel and is accommodated in a cylindrical acoustic tube (a tubular member). Further, the speaker device is configured such that a component of a low sound range among the sounds generated at the back side of the speaker resonates in the acoustic tube and is emitted from a lower surface of the instrument panel.